Optical scanner

Abstract

To provide a sufficiently small optical scanner.SOLUTION: An optical scanner comprises: a deflector that deflects a first light beam from a first light source and scans a first surface to be scanned in a main scanning direction; a first image forming optical system including one or more image forming optical elements that guide the first light beam deflected on a first deflection surface of the deflector to the first surface to be scanned; and a first reflection optical element that is arranged between the deflector and a first image forming optical element closest to the deflector among at least one image forming optical element included in the first image forming optical system, on an optical path of the first light beam from the deflector to the first surface to be scanned, and that reflects the first light beam. When the optical path length between the first surface to be scanned and a first on-axis deflection point of the first deflection surface on an optical axis of the first image forming optical system is defined as Tc1, and the distance between the first surface to be scanned and the most off-axis image height as h1, the condition of 0.50≤Tc1 / h1≤1.00 is satisfied.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an optical scanning device, and more particularly to an optical scanning device suitably used in an image forming apparatus such as a laser beam printer, a digital copying machine, or a multifunction printer (multifunctional printer).

Background Art

[0002] Conventionally, as disclosed in Patent Document 1 for example, an optical scanning device has been known in which a reflecting optical element is disposed between a deflector and the imaging optical element closest to the deflector among at least one imaging optical element included in an imaging optical system to achieve miniaturization.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the optical scanning device disclosed in Patent Document 1, the optical path length between the deflector and the surface to be scanned has not been studied, and the miniaturization is not sufficient. Therefore, an object of the present invention is to provide a sufficiently compact optical scanning device.

Means for Solving the Problems

[0005] The optical scanning device according to the present invention includes a deflector that deflects a first light beam from a first light source to scan a first scanned surface in a main scanning direction, and a first imaging optical system that includes at least one imaging optical element that guides the first light beam deflected by a first deflection surface of the deflector to the first scanned surface. On the optical path of the first light beam from the deflector to the first scanned surface, it is disposed between the deflector and a first imaging optical element closest to the deflector among at least one imaging optical element included in the first imaging optical system, and includes a first reflective optical element that reflects the first light beam. The optical path length between a first on-axis deflection point of the first deflection surface on the optical axis of the first imaging optical system and the first scanned surface is T c1 , and the distance between the outermost image heights of the first scanned surface is h 1 When it is set as such, 0.50 ≦ T c1 / h 1 ≦ 1.00 It is characterized by satisfying the condition.

Effect of the Invention

[0006] According to the present invention, a sufficiently small optical scanning device can be provided.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0008] Hereinafter, the optical scanning device according to the present embodiment will be described in detail with reference to the accompanying drawings. Note that the drawings shown below may be drawn at scales different from the actual ones for easy understanding of the present embodiment.

[0009] Also, in the following description, the main scanning direction is the direction perpendicular to the rotation axis of the deflection element 104 and the optical axis of the imaging optical system 85 (the direction in which the light beam is deflected by the deflection element 104), and the sub-scanning direction is the direction parallel to the rotation axis of the deflection element 104. The main scanning cross-section is a cross-section perpendicular to the sub-scanning direction, and the sub-scanning cross-section is a cross-section perpendicular to the main scanning direction. Also, hereinafter, the direction parallel to the optical axis of the imaging optical system 85 is defined as the X direction, the main scanning direction is defined as the Y direction, and the sub-scanning direction is defined as the Z direction.

[0010] [First Embodiment] Conventionally, in order to reduce the size of products equipped with an optical scanning device such as an image forming apparatus, in the optical scanning device, a configuration in which the optical path of a light beam deflected by a deflector is bent by a folding mirror has been used. Various techniques have also been proposed to reduce the size of the housing itself in which the optical elements that form an optical scanning device are housed by disposing a folding mirror between a deflector and an imaging optical element closest to the deflector.

[0011] However, in a conventional optical scanning device in which a folding mirror is disposed between a deflector and an imaging optical element closest to the deflector, the distance between the deflector and the surface to be scanned, that is, the optical path length of the imaging optical system, has not been studied, and sufficient miniaturization has not been achieved. Therefore, an object of the present embodiment is to provide an optical scanning device capable of achieving sufficient miniaturization by reducing the optical path length in the imaging optical system.

[0012] FIG. 1(a) shows a developed view of a schematic main scanning cross section of an optical scanning device 100 according to the first embodiment. FIGS. 1(b) and (c) show partial schematic sub-scanning cross-sectional views of the optical scanning device 100 according to the first embodiment.

[0013] The optical scanning device 100 according to the present embodiment includes a housing 10, a deflector unit 12 (deflector), a light source 101 (first light source), a diaphragm 102, an incident optical element 103 (first incident optical element), a folding mirror 105 (first reflective optical element), and an imaging optical element 106. In the optical scanning device 100 according to the present embodiment, an incident optical system 75 (first incident optical system) is formed by the diaphragm 102 and the incident optical element 103, and an imaging optical system 85 (first imaging optical system) is formed by the imaging optical element 106. In the optical scanning device 100 according to the present embodiment, a reflective optical system 95 (first reflective optical system) is formed by the folding mirror 105.

[0014] That is, in the optical scanning device 100 according to the present embodiment, the imaging optical system 85 consists only of the imaging optical element 106, in other words, it is formed by a single imaging optical element 106. However, in the optical scanning device 100 according to the present embodiment, the imaging optical system 85 only needs to be formed of at least one imaging optical element.

[0015] In the optical scanning device 100 according to the present embodiment, the reflection optical system 95 that reflects the light beam deflected by the deflection element unit 12 is composed only of the folding mirror 105, that is, it is formed by a single folding mirror 105. That is, in the optical scanning device 100 according to the present embodiment, no folding mirror other than the folding mirror 105 is arranged on the optical path of the light beam from the deflection element unit 12 to the scanned surface 107.

[0016] The housing 10 houses each of the above optical elements that form the optical scanning device 100 according to the present embodiment. As the light source 101, for example, a semiconductor laser can be used, and the number of light emitting portions of the light source 101 may be one or a plurality. The aperture 102 has an elliptical opening, and limits the beam width in the main scanning direction and the sub-scanning direction of the light beam (the first light beam) emitted from the light source 101.

[0017] The incident optical element 103 has a positive refractive power in the main scanning section, and converts the light beam that has passed through the aperture 102 into a converging light beam in the main scanning section. By converting the light beam emitted from the light source 101 into a converging light beam in the main scanning section in this way, it is possible to achieve a good balance between shortening the optical path and optical performance in the imaging optical system 85 formed by only the single imaging optical element 106.

[0018] The incident optical element 103 also has a positive refractive power in the sub-scanning section, and by condensing the light beam that has passed through the aperture 102 near the deflection surface 104a of the deflection element 104, a line image that is long in the main scanning direction is formed near the deflection surface 104a. In the optical scanning device 100 according to the present embodiment, within the main scanning cross section, the beam width of the light beam when incident on the deflection element 104 is smaller than the width of the deflection surface 104a of the deflection element 104.

[0019] The deflection element unit 12 is formed from a deflection element 104 having a plurality of deflection surfaces 104a, a motor 104b (drive unit) necessary for rotating the deflection element 104 around the rotation axis, and a motor substrate 104c (drive unit). In the deflection element unit 12, the deflection element 104 rotates at a constant speed by the motor 104b.

[0020] The folding mirror 105 is, for example, a plane mirror. The folding mirror 105 is disposed between the deflection element unit 12 and the imaging optical element 106, which is the imaging optical element closest to the deflection element unit 12 among at least one imaging optical element included in the imaging optical system 85, on the optical path of the light beam deflected by the deflection element unit 12. The folding mirror 105 reflects the light beam deflected by the deflection surface 104a of the deflection element 104 toward the imaging optical element 106 without changing the convergence degree.

[0021] In the optical scanning device 100 according to the present embodiment, the optical path of the light beam deflected by the deflection surface 104a of the deflection element 104 is bent by 90 degrees within the sub-scanning cross section by the folding mirror 105. In other words, in the optical scanning device 100 according to the present embodiment, the incident angle of the light beam on the reflection surface of the folding mirror 105 (the angle formed by the incident direction of the light beam with respect to the normal of the reflection surface) is 45 degrees.

[0022] The imaging optical element 106 has two optical surfaces (lens surfaces), an incident surface (first surface) and an exit surface (second surface), and has a positive refractive power within both the main scanning cross section and the sub-scanning cross section. As a result, the light beam incident on the imaging optical element 106 is condensed within both the main scanning cross section and the sub-scanning cross section, and a spot-like image is formed in the vicinity of the scanned surface 107 (first scanned surface).

[0023] The imaging optical element 106 is configured such that a light beam deflected by the deflection surface 104a of the deflection element 104 in the main scanning cross-section scans the surface to be scanned 107 with desired scanning characteristics. Also, the imaging optical element 106 sets the vicinity of the deflection surface 104a of the deflection element 104 and the vicinity of the surface to be scanned 107 in the sub-scanning cross-section to an optically conjugate relationship with each other. Thereby, so-called surface tilt compensation can be performed to reduce the deviation of the scanning position in the sub-scanning direction on the surface to be scanned 107 when the deflection surface 104a tilts.

[0024] In the optical scanning device 100 according to the present embodiment, the light beam emitted from the light source 101 is guided by the incident optical system 75 to the deflection surface 104a (first deflection surface) of the deflection element 104. Next, the light beam deflected by the deflection surface 104a of the deflection element 104 is reflected by the folding mirror 105 and then guided (condensed) onto the surface to be scanned 107 by the imaging optical element 106.

[0025] Then, the motor 104b rotates the deflection element 104 at a constant speed, causing the light beam to scan the surface to be scanned 107 in the direction of arrow Sc, and an electrostatic latent image is formed on the surface to be scanned 107. In the optical scanning device 100 according to the present embodiment, the angle between the optical axis of the incident optical system 75 and the optical axis of the imaging optical system 85 in the main scanning cross-section is 90 degrees.

[0026] As described above, in the optical scanning device 100 according to the present embodiment, the folding mirror 105 is disposed upstream of the imaging optical element 106 on the optical path of the light beam deflected by the deflection surface 104a of the deflection element 104. Thereby, the optical path length between the deflection surface 104a and the reflection surface of the folding mirror 105 can be shortened as compared with a general configuration in which the folding mirror 105 is disposed downstream of the imaging optical element 106 on the optical path. That is, by reducing the size in the main scanning cross section of the optical scanning device 100 according to the present embodiment, it becomes possible to reduce the size of the housing 10.

[0027] Also, in the optical scanning device 100 according to the present embodiment, as shown in FIG. 1(c), the folding mirror 105 reflects the incident light beam downward in the sub-scanning direction, that is, toward the side where the motor 104b and the motor substrate 104c are arranged with respect to the deflection element 104. Thereby, it becomes possible to arrange the imaging optical element 106 in the inefficient space formed by the motor 104b and the motor substrate 104c other than the deflection element 104 in the deflection element unit 12. That is, by reducing the size in the sub-scanning cross section of the optical scanning device 100 according to the present embodiment, it becomes possible to further reduce the size of the housing 10.

[0028] Also, in the optical scanning device 100 according to the present embodiment, a light beam deflected to a predetermined scanning angle by the deflection surface 104a of the deflection element 104 is guided to a synchronization detection sensor by a synchronization detection optical system (not shown), thereby generating a synchronization detection signal. And based on the generated synchronization detection signal, the rotation speed of the deflection element 104 is controlled to be constant.

[0029] Note that plastic molded lenses formed by injection molding are used for the incident optical element 103 and the imaging optical element 106 provided in the optical scanning device 100 according to the present embodiment, but the present invention is not limited thereto, and glass molded lenses may be used. Since the molded lens is easy to form an aspherical shape and is suitable for mass production, by using the molded lens for the incident optical element 103 and the imaging optical element 106, it is possible to improve productivity and optical performance.

[0030] Also, the folding mirror 105 provided in the optical scanning device 100 according to the present embodiment is formed by forming a reflective surface on a general long glass, but is not limited thereto. That is, the folding mirror 105 may be formed by forming a reflective surface on a member formed of a plastic mold or by performing mirror finishing on a metal such as aluminum. Further, although the reflective surface of the folding mirror 105 is formed in a planar shape, it may be formed in a shape such as a spherical surface.

[0031] Next, the specifications of the optical scanning device 100 according to the present embodiment, the refractive indices and surface intervals of the respective optical elements, and the lens surface shapes of the incident optical element 103 and the imaging optical element 106 are shown in Tables 1, 2, and 3 below, respectively.

[0032]

Table 1

[0033]

Table 2

[0034]

Table 3

[0035] The incident surface of the incident optical element 103 provided in the optical scanning device 100 according to the present embodiment is a diffractive surface on which a diffraction grating is formed. The incident optical element 103 is formed by injection molding using a plastic material, and a so-called temperature compensation optical system is employed that compensates for changes in refractive power due to environmental variations with changes in refractive power due to changes in the wavelength of the semiconductor laser. Specifically, the diffractive surface formed on the incident surface of the incident optical element 103 is defined by a phase function represented by the following equation (1).

Equation

[0036] In Equation (1), φ is the phase correlation function, and M is the diffraction order. In the optical scanning device 100 according to the present embodiment, since the first-order diffracted light is used, the diffraction order M is 1. Also, λ is the wavelength of the light beam emitted from the light source 101. In the optical scanning device 100 according to the present embodiment, the wavelength λ is 790 nanometers.

[0037] In addition, the shapes (generatrix shapes) in the main scanning cross sections of the incident surface and the exit surface of the imaging optical element 106 provided in the optical scanning device 100 according to the present embodiment each have an aspherical shape defined by a function of a tenth-degree polynomial represented by the following Equation (2).

Equation

[0038] In Equation (2), the intersection point of each optical surface of the imaging optical element 106 and the optical axis is taken as the origin, the direction parallel to the optical axis is the X direction, and the direction perpendicular to the optical axis in the main scanning cross section is the Y direction. Also, in Equation (2), R is the generatrix curvature radius, K is the eccentricity, and B 1 to B 10 are the aspherical coefficients. Also, for the coefficients whose numerical values are different between the light source side (the +Y direction side) and the anti-light source side (the -Y direction side) among the aspherical coefficients B 1 to B 10 the numerical values on each side are shown.

[0039] In addition, the shapes (filament shapes) in the sub-scanning cross sections of the incident surface and the exit surface of the imaging optical element 106 provided in the optical scanning device 100 according to the present embodiment are each represented by the following Equation (3).

Equation

[0040] In Equation (3), S is the shape (filament shape) in the cross section including the normal line of the generatrix at a predetermined position in the main scanning direction and perpendicular to the main scanning cross section. In addition, the radius of curvature (sub-ray radius of curvature) r' in the sub-scanning cross-section at a position separated from the optical axis by Y in the main scanning direction is expressed by the following formula (4).

Equation

[0041] In formula (4), r is the sub-ray radius of curvature on the optical axis, and E 1 to E 10 is the sub-ray change coefficient. As shown in formula (4), the sub-ray radius of curvature r' changes depending on the position Y in the main scanning direction. In the optical scanning device 100 according to the present embodiment, the shape of the optical surface of each optical element is defined by a function represented by the above formulas (1) to (4), but it is not limited thereto and may be defined by another function.

[0042] Next, the non-uniform scanning in the optical scanning device 100 according to the present embodiment will be described. The scanning characteristics of the imaging optical system 85 provided in the optical scanning device 100 according to the present embodiment are represented by the following formula (5).

Equation

[0043] In formula (5), θ is the scanning angle by the deflection element 104, and Y is the coordinate (image height) in the main scanning direction of the condensing position on the scanned surface 107 of the light beam deflected by the scanning angle θ. Also in formula (5), KK is the imaging coefficient at the on-axis image height, and α is the scanning characteristic coefficient for determining the scanning characteristics of the imaging optical system 85.

[0044] In the optical scanning device 100 according to the present embodiment, the on-axis image height is the image height (Y = 0) on the optical axis of the imaging optical system 85 and corresponds to the scanning angle θ = 0. The off-axis image height is the image height other than the on-axis image height (Y ≠ 0) and corresponds to the scanning angle θ ≠ 0. The outermost off-axis image height is the image height when the scanning angle θ is maximum.

[0045] The imaging coefficient KK corresponds to the coefficient f in the scanning characteristic (fθ characteristic) Y = fθ when a perfect parallel light beam is incident on the imaging optical system 85. That is, the imaging coefficient KK is a coefficient for making the image height Y and the scanning angle θ proportional to each other in the same manner as the fθ characteristic when a light beam other than a perfect parallel light beam is incident on the imaging optical system 85. In the optical scanning device 100 according to the present embodiment, a converging light beam in the main scanning plane is incident on the imaging optical system 85, and the imaging coefficient KK in the scanning characteristic of the imaging optical system 85 is set in response to the incidence of the converging light beam.

[0046] In the optical scanning device 100 according to the present embodiment, the scanning characteristic coefficient α is set to a positive value. For example, when the value of the scanning characteristic coefficient α is 0, since the formula (5) is expressed as Y = KK·θ, the scanning characteristic of the imaging optical system 85 is the same as the scanning characteristic Y = fθ of a general imaging optical system.

[0047] Also, by differentiating both sides of the formula (5) with respect to the scanning angle θ, the scanning speed of the light beam at a predetermined image height on the scanned surface 107 corresponding to a predetermined scanning angle θ, as represented by the following formula (6), can be obtained.

Equation

[0048] Then, by dividing both sides of the formula (6) by the scanning speed dY / dθ = KK at the on-axis image height, the following formula (7) is obtained.

Equation

[0049] The right side of the formula (7) represents the deviation amount of the scanning speed at each off-axis image height with respect to the scanning speed at the on-axis image height, in other words, the deviation amount of the partial magnification at each off-axis image height with respect to the partial magnification at the on-axis image height, that is, the partial magnification deviation. Therefore, when the value of the scanning characteristic coefficient α is non-zero as in the imaging optical system 85 provided in the optical scanning device 100 according to the present embodiment, the scanning speeds of the light beams differ between the on-axis image height and the off-axis image height. In the optical scanning device 100 according to the present embodiment, by setting the scanning characteristic such that the value of the scanning characteristic coefficient α is non-zero in the imaging optical system 85, shortening of the optical path length of the imaging optical system 85 is realized.

[0050] FIG. 2 shows the partial magnification deviation at each image height in the optical scanning device 100 according to the present embodiment. Specifically, in FIG. 2, the value of the ratio of the partial magnification at each off-axis image height to the partial magnification at the on-axis image height is shown. As shown in FIG. 2, in the optical scanning device 100 according to the present embodiment, the maximum partial magnification deviation occurs at the outermost off-axis image height, specifically, a partial magnification deviation of about 130.6%.

[0051] That is, in the optical scanning device 100 according to the present embodiment, the scanning characteristics of the imaging optical system 85 are set such that the scanning speed at each off-axis image height is higher than the scanning speed at the on-axis image height. In other words, in the optical scanning device 100 according to the present embodiment, the scanning speed of the light beam on the surface to be scanned 107 increases monotonically from the on-axis image height toward the outermost off-axis image height.

[0052] As described above, in the optical scanning device 100 according to the present embodiment, the incident optical element 103 has a positive refractive power in the main scanning plane and converts the incident light beam into a converging light beam in the main scanning plane. Specifically, in the optical scanning device 100 according to the present embodiment, when the imaging optical system 85 is not virtually provided, the optical path length D m between the on-axis deflection point (first on-axis deflection point) and the position where the on-axis light beam naturally converges in the main scanning plane is about 229 mm.

[0053] Here, the on-axis light beam is a light beam that scans the on-axis image height on the scanned surface 107, and the on-axis deflection point is the deflection point of the principal ray of the on-axis light beam on the deflection surface 104a of the deflection element 104. In the optical scanning device 100 according to the present embodiment, by setting the degree of convergence in the principal scanning cross-section of the light beam by the incident optical element 103 stronger than before, even if the imaging optical element 106 is arranged at a distance from the deflection element 104 while having a short optical path, it is possible to maintain good optical performance.

[0054] FIGS. 3(a) and (b) respectively show the image height dependence of the depth center position of the line spread function (LSF) in the principal scanning direction and the depth center position of the LSF in the sub-scanning direction on the scanned surface 107 in the optical scanning device 100 according to the present embodiment. Note that the depth center position of the LSF in the principal scanning direction and the depth center position of the LSF in the sub-scanning direction as used herein respectively refer to the center positions of regions where the LSF widths in the principal scanning direction and the sub-scanning direction become equal to or less than the slice level when defocused in the optical axis direction in the vicinity of the scanned surface 107.

[0055] In the optical scanning device 100 according to the present embodiment, the slice level is set to 120 micrometers over the entire image height in both the principal scanning direction and the sub-scanning direction. Also, the LSF width in the principal scanning direction and the LSF width in the sub-scanning direction respectively refer to the widths when the light quantity profiles obtained by integrating the spot profiles in the sub-scanning direction and the principal scanning direction at each image height are sliced at the position of 13.5% of the maximum value. As shown in FIGS. 3(a) and (b), both the depth center position of the LSF in the principal scanning direction and the depth center position of the LSF in the sub-scanning direction are within ±1 mm over the entire image height, and it can be seen that good imaging performance is achieved in the optical scanning device 100 according to the present embodiment.

[0056] Also, in the optical scanning device 100 according to the present embodiment, the following conditional expression (8) is satisfied.

Equation

[0057] In conditional expression (8), T c is the optical path length along the optical axis of the imaging optical system 85 between the on-axis deflection point on the deflection surface 104a of the deflection element 104 and the surface to be scanned 107, and h is the scanning width in the main scanning direction on the surface to be scanned 107, in other words, the distance between the outermost image heights on the surface to be scanned 107. If it exceeds the upper limit value of conditional expression (8), since the optical path length of the imaging optical system 85 increases, it becomes difficult to sufficiently achieve miniaturization of the optical scanning device 100 according to the present embodiment. On the other hand, if it is below the lower limit value of conditional expression (8), since the optical path length of the imaging optical system 85 decreases, it becomes difficult to maintain good imaging performance in the optical scanning device 100 according to the present embodiment.

[0058] In the optical scanning device 100 according to the present embodiment, it is preferable that the following conditional expression (8a) is satisfied.

Equation

[0059] In the optical scanning device 100 according to the present embodiment, it is preferable that the following conditional expressions (9), (10), and (11) are satisfied.

Equation

Equation

Equation

[0060] In conditional expression (9), D m is the optical path length between the on-axis deflection point and the position (natural convergence point, first convergence point) where the on-axis light beam deflected by the deflection surface 104a of the deflection element 104 converges in the main scanning cross-section when the imaging optical system 85 is not provided. If it exceeds the upper limit value or is below the lower limit value of conditional expression (9), it becomes difficult to balance the refractive power sharing in the imaging optical system 85, and it becomes difficult to maintain good imaging performance. Also, if it is below the lower limit value of conditional expression (9), there is also a drawback that the sensitivity of the irradiation position shift in the main scanning direction due to the assembly error of the deflection element 104 increases.

[0061] Also, in conditional expression (10), f s and f m are the focal lengths in the sub-scanning cross-section and the main-scanning cross-section on the optical axis of the imaging optical system 85, respectively. If it exceeds the upper limit value or is below the lower limit value of conditional expression (10), it becomes difficult to realize the shapes in the main-scanning cross-section and the sub-scanning cross-section of the imaging optical element 106 that forms an imaging optical system 85 with a balance for optical performance.

[0062] Also, in conditional expression (11), D R2 is the optical path length along the optical axis of the imaging optical system 85 between the on-axis deflection point of the deflection element 104 and the exit surface of the imaging optical element 106. If it exceeds the upper limit value of conditional expression (11), since the imaging optical element 106 is too separated from the deflection element 104, it becomes difficult to sufficiently achieve miniaturization of the optical scanning device 100 according to the present embodiment. On the other hand, if it is below the lower limit value of conditional expression (11), since the imaging optical element 106 is too close to the deflection element 104, it becomes difficult to arrange the folding mirror 105.

[0063] In the optical scanning device 100 according to the present embodiment, it is more preferable that the following conditional expressions (9a), (10a), and (11a) are satisfied.

Equation

Equation

Equation

[0064] In the optical scanning device 100 according to the present embodiment, it is preferable that the following conditional expression (12) is satisfied.

Equation

[0065] In the conditional expression (12), ΔY(%) is the value of the ratio of the partial magnification at the outermost off-axis image height to the partial magnification at the on-axis image height.

[0066] In the optical scanning device 100 according to the present embodiment, it is more preferable that the following conditional expression (12a) is satisfied.

Equation

[0067] In the optical scanning device 100 according to the present embodiment, T c / h = 0.58, D m / T c = 1.83 and f s / f m = 0.11, and the conditional expressions (8), (8a), (9), (9a), (10) and (10a) are satisfied. In the optical scanning device 100 according to the present embodiment, D R2 / T c = 0.23 and |ΔY| = 130.6%, and the conditional expressions (11), (11a), (12) and (12a) are satisfied.

[0068] As described above, in the optical scanning device 100 according to the present embodiment, the folding mirror 105 is disposed between the deflection element unit 12 and the imaging optical element 106 closest to the deflection element unit 12 in the imaging optical system 85, and the conditional expression (8) is satisfied. Thereby, it is possible to provide the optical scanning device 100 which is sufficiently miniaturized by shortening the optical path.

[0069] In the optical scanning device 100 according to the present embodiment, a coupling lens and a cylindrical lens may be provided instead of the incident optical element 103.

[0070] [Second Embodiment] FIG. 4(a) shows a schematic main scanning cross-sectional unfolded view of the optical scanning device 200 according to the second embodiment. FIGS. 4(b) and 4(c) show partial schematic sub-scanning cross-sectional views of the optical scanning device 200 according to the second embodiment. In the following, the description of the same configuration as that of the optical scanning device 100 according to the first embodiment will be omitted.

[0071] The optical scanning device 200 according to the present embodiment includes a housing 10, a deflection element unit 12, first and second light sources 101a and 101b, and first and second apertures 102a and 102b. The optical scanning device 200 according to the present embodiment further includes first and second incident optical elements 103a and 103b, first and second folding mirrors 105a and 105b, and first and second imaging optical elements 106a and 106b.

[0072] In the optical scanning device 200 according to the present embodiment, a first incident optical system is formed by the first aperture 102a and the first incident optical element 103a, and a second incident optical system is formed by the second aperture 102b and the second incident optical element 103b. In the optical scanning device 200 according to the present embodiment, a first imaging optical system is formed by the first imaging optical element 106a, and a second imaging optical system is formed by the second imaging optical element 106b (third imaging optical element). In the optical scanning device 200 according to the present embodiment, a first reflection optical system is formed by the first folding mirror 105a, and a second reflection optical system is formed by the second folding mirror 105b (second reflection optical element).

[0073] As the first and second light sources 101a and 101b, for example, semiconductor lasers can be used, and the number of light emitting portions of the first and second light sources 101a and 101b may be one or more. The first and second diaphragms 102a and 102b have elliptical openings, and limit the beam widths of the first and second light beams emitted from the first and second light sources 101a and 101b in the main scanning direction and the sub-scanning direction, respectively.

[0074] The first and second incident optical elements 103a and 103b have positive refractive power in the main scanning section, and convert the first and second light beams that have passed through the first and second diaphragms 102a and 102b into convergent light beams in the main scanning section. Thereby, it becomes possible to achieve a good balance between shortening the optical path length and optical performance in the first and second imaging optical systems formed by the single first and second imaging optical elements 106a and 106b, respectively.

[0075] Also, the first and second incident optical elements 103a and 103b have positive refractive power in the sub-scanning section. Therefore, the first and second light beams that have passed through the first and second diaphragms 102a and 102b are condensed in the vicinity of the first and second deflection surfaces 104a1 and 104a2 of the deflection element 104.

[0076] Thereby, a line image that is long in the main scanning direction is formed in the vicinity of the first and second deflection surfaces 104a1 and 104a2. In the optical scanning device 200 according to the present embodiment, in the main scanning section, the beam widths of the first and second light beams when incident on the deflection element 104 are smaller than the widths of the first and second deflection surfaces 104a1 and 104a2 of the deflection element 104, respectively.

[0077] The first and second folding mirrors 105a and 105b are, for example, plane mirrors. The first and second folding mirrors 105a and 105b reflect the first and second light beams deflected by the first and second deflection surfaces 104a1 and 104a2 of the deflection element 104 toward the first and second imaging optical elements 106a and 106b without changing the degree of convergence. The optical paths of the first and second light beams deflected by the first and second deflection surfaces 104a1 and 104a2 of the deflection element 104 are bent by 90° in the sub-scanning cross section by the first and second folding mirrors 105a and 105b.

[0078] The first and second imaging optical elements 106a and 106b have two optical surfaces (lens surfaces), an incident surface (first surface) and an exit surface (second surface), and have a positive refractive power in both the main scanning cross section and the sub-scanning cross section. As a result, the first and second light beams incident on the first and second imaging optical elements 106a and 106b are condensed in both the main scanning cross section and the sub-scanning cross section, so that spot-like images are formed in the vicinity of the first and second surfaces to be scanned 107a and 107b, respectively.

[0079] The first and second imaging optical elements 106a and 106b are configured such that the first and second light beams deflected by the first and second deflection surfaces 104a1 and 104a2 scan the first and second surfaces to be scanned 107a and 107b with desired scanning characteristics. Also, the first and second imaging optical elements 106a and 106b respectively set the vicinity of the first and second deflection surfaces 104a1 and 104a2 of the deflection element 104 and the vicinity of the first and second surfaces to be scanned 107a and 107b in an optically conjugate relationship in the sub-scanning cross section. Thereby, so-called surface tilt compensation can be performed to reduce the deviation of the scanning position in the sub-scanning direction on the first and second surfaces to be scanned 107a and 107b when the first and second deflection surfaces 104a1 and 104a2 are tilted.

[0080] In the optical scanning device 200 according to the present embodiment, the first light beam emitted from the first light source 101a is guided by the first incident optical system to the first deflection surface 104a1 of the deflection element 104. Next, the first light beam deflected by the first deflection surface 104a1 of the deflection element 104 is reflected by the first folding mirror 105a, and then is guided (condensed) onto the first scanned surface 107a by the first imaging optical element 106a. Then, as the motor 104b rotates the deflection element 104 at a constant speed, the first light beam scans the first scanned surface 107a in the direction of arrow Sc, and an electrostatic latent image is formed on the first scanned surface 107a.

[0081] Also, in the optical scanning device 200 according to the present embodiment, the second light beam emitted from the second light source 101b is guided by the second incident optical system to the second deflection surface 104a2 of the deflection element 104. Next, the second light beam deflected by the second deflection surface 104a2 of the deflection element 104 is reflected by the second folding mirror 105b, and then is guided (condensed) onto the second scanned surface 107b by the second imaging optical element 106b. Then, as the motor 104b rotates the deflection element 104 at a constant speed, the second light beam scans the second scanned surface 107b in the direction of arrow Sc', and an electrostatic latent image is formed on the second scanned surface 107b.

[0082] As described above, the optical scanning device 200 according to the present embodiment employs a so-called opposed (both-side) scanning system in which the first and second light beams scan the first and second scanned surfaces 107a and 107b provided on opposite (different) sides with respect to the deflection element unit 12.

[0083] Next, the specifications of the optical scanning device 200 according to the present embodiment, the refractive indices and surface intervals of the respective optical elements, and the lens surface shapes of the first incident optical element 103a and the first imaging optical element 106a are shown in Tables 4, 5, and 6 below, respectively. In the optical scanning device 200 according to the present embodiment, with respect to the deflection element 104, the configurations of the first and second incident optical systems are symmetric to each other, and the configurations of the first and second imaging optical systems are symmetric to each other.

[0084] Therefore, in Tables 4 to 6, only the configurations of the first incident optical system and the first imaging optical system are shown, and the configurations of the second incident optical system and the second imaging optical system are omitted. Note that the effects of the present embodiment described below can also be obtained even if the configurations of the first and second incident optical systems are asymmetric to each other and the configurations of the first and second imaging optical systems are asymmetric to each other.

[0085]

Table 4

[0086]

Table 5

[0087]

Table 6

[0088] In the optical scanning device 200 according to the present embodiment, the first and second folding mirrors 105a and 105b reflect the incident first and second light beams toward the upper side in the sub-scanning direction, that is, the side where the motors 104b and the motor substrate 104c are not arranged with respect to the deflection element 104. By arranging the imaging optical element 106 above the folding mirror 105 in the sub-scanning direction in this way, the assembly of each optical element in the housing 10 becomes easy. Specifically, from the viewpoints of the width of each optical element in the main scanning direction of the effective region and the configuration of the support portion when assembling each optical element from the upper side (open portion) of the housing 10, it becomes easy to miniaturize the housing 10 in the main scanning cross section.

[0089] FIG. 5 shows the partial magnification deviation at each image height in the optical scanning device 200 according to the present embodiment. As shown in FIG. 5, in the optical scanning device 200 according to the present embodiment, the maximum partial magnification deviation occurs at the outermost image height, specifically, a partial magnification deviation of about 130.6% occurs. That is, in the optical scanning device 200 according to the present embodiment, similar to the optical scanning device 100 according to the first embodiment, the scanning characteristics of the imaging optical system 85 are set such that the scanning speed at each off-axis image height is higher than the scanning speed at the on-axis image height.

[0090] As described above, in the optical scanning device 200 according to the present embodiment, the first and second incident optical elements 103a and 103b each have a positive refractive power in the main scanning plane, and convert the incident first and second light beams into convergent light beams in the main scanning plane. Specifically, in the optical scanning device 200 according to the present embodiment, when the first and second imaging optical systems are not virtually provided, the optical path length D m between the on-axis deflection point and the position where the on-axis light beam naturally converges in the main scanning plane is about 241.8 mm.

[0091] FIGS. 6(a) and (b) show the image height dependence of the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position on the first scanned surface 107a in the optical scanning device 200 according to the present embodiment, respectively. As shown in FIGS. 6(a) and (b), both the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position are within ±1 mm over the entire image height, indicating that good imaging performance is achieved in the optical scanning device 200 according to the present embodiment.

[0092] In the optical scanning device 200 according to the present embodiment, the following conditional expressions (8') and (8'') corresponding to the above conditional expression (8) are satisfied.

Equation

Equation

[0093] In conditional expression (8’), T c1 is the optical path length between the on-axis deflection point (first on-axis deflection point) on the first deflection surface 104a1 on the optical axis of the first imaging optical system and the first scanned surface 107a, and h 1 is the distance between the outermost image heights of the first scanned surface 107a. Also, in conditional expression (8’’), T c2 is the optical path length between the on-axis deflection point (second on-axis deflection point) on the second deflection surface 104a2 on the optical axis of the second imaging optical system and the second scanned surface 107b, and h 2 is the distance between the outermost image heights of the second scanned surface 107b.

[0094] Note that in the optical scanning device 200 according to the present embodiment, it is preferable that the following conditional expressions (8a’) and (8a’’) are satisfied.

Number

Number

[0095] Also, in the optical scanning device 200 according to the present embodiment, it is preferable that the following conditional expressions (9’) and (9’’) corresponding to the above conditional expression (9) and the following conditional expressions (10’) and (10’’) corresponding to the above conditional expression (10) are satisfied. Also, in the optical scanning device 200 according to the present embodiment, it is preferable that the following conditional expressions (11’) and (11’’) corresponding to the above conditional expression (11) are satisfied.

Number

Number

Number

Number

[0096] In conditional expression (9’), D m1 is the optical path length between the on-axis deflection point on the first deflection surface 104a1 when the first imaging optical system is not provided and the position (first convergence point) where the first light beam deflected by the first deflection surface 104a1 converges within the main scanning cross-section. Also, in conditional expression (9’’), D m2 is the optical path length between the on-axis deflection point on the second deflection surface 104a2 when the second imaging optical system is not provided and the position (second convergence point) where the second light beam deflected by the second deflection surface 104a2 converges within the main scanning cross-section.

[0097] Also, in conditional expression (10’), f s1 and f m1 are the focal lengths in the sub-scanning cross-section and the main scanning cross-section of the first imaging optical system, respectively. Also, in conditional expression (10’’), f s2 and f m2 are the focal lengths in the sub-scanning cross-section and the main scanning cross-section of the second imaging optical system, respectively.

[0098] Also, in conditional expression (11’), D R2_1 is the optical path length between the on-axis deflection point on the first deflection surface 104a1 on the optical axis of the first imaging optical system and the exit surface of a predetermined imaging optical element (second imaging optical element). Here, the predetermined imaging optical element refers to the imaging optical element that is the farthest from the deflection element unit 12 among at least one imaging optical element included in the first imaging optical system on the optical path of the first light beam deflected by the first deflection surface 104a1. That is, in the optical scanning device 200 according to the present embodiment, the predetermined imaging optical element is the first imaging optical element 106a.

[0099] Also, in conditional expression (11''), D R2_2 is the optical path length between the on-axis deflection point on the second deflection plane 104a2 on the optical axis of the second imaging optical system and the exit surface of a predetermined imaging optical element (the second imaging optical element). Here, the predetermined imaging optical element refers to the imaging optical element that is farthest from the deflection element unit 12 among at least one imaging optical element included in the second imaging optical system on the optical path of the second light beam deflected by the second deflection plane 104a2. That is, in the optical scanning device 200 according to the present embodiment, the predetermined imaging optical element is the second imaging optical element 106b.

[0100] In the optical scanning device 200 according to the present embodiment, it is more preferable that the following conditional expressions (9a'), (9a''), (10a'), (10a''), (11a') and (11a'') are satisfied.

Number

Number

Number

Number

Number

Number

[0101] In the optical scanning device 200 according to the present embodiment, it is preferable that the following conditional expressions (12') and (12''), which correspond to the above conditional expression (12), are satisfied.

Number

Number

[0102] In conditional expression (12’), ΔY 1 (%) is the value of the ratio of the partial magnification at the outermost axial image height to the partial magnification at the axial image height on the first scanned surface 107a. Also, in conditional expression (12’’), ΔY 2 (%) is the value of the ratio of the partial magnification at the outermost axial image height to the partial magnification at the axial image height on the second scanned surface 107b.

[0103] In the optical scanning device 200 according to the present embodiment, it is more preferable that the following conditional expressions (12a’) and (12a’’) are satisfied.

Equation

Equation

[0104] In the optical scanning device 200 according to the present embodiment, T c1 / h 1 = T c2 / h 2 = 0.65, and conditional expressions (8’), (8a’), (8’’), and (8a’’) are satisfied. Also, in the optical scanning device 200 according to the present embodiment, D m1 / T c1 = D m2 / T c2 = 1.73, and conditional expressions (9’), (9a’), (9’’), and (9a’’) are satisfied. Also, in the optical scanning device 200 according to the present embodiment, f s1 / f m1 = f s2 / f m2 = 0.15, and conditional expressions (10’), (10a’), (10’’), and (10a’’) are satisfied. Also, in the optical scanning device 200 according to the present embodiment, D R2_1 / T c1 = D R2_2 / Tc2 It is 0.30, and the conditional expressions (11’), (11a’), (11’’) and (11a’’) are satisfied. Also, in the optical scanning device 200 according to the present embodiment, |ΔY 1 | = |ΔY 2 | = 130.6%, and the conditional expressions (12’), (12a’), (12’’) and (12a’’) are satisfied.

[0105] As described above, in the optical scanning device 200 according to the present embodiment, the first folding mirror 105a is disposed between the deflection element unit 12 and the first imaging optical element 106a that is closest to the deflection element unit 12 in the first imaging optical system. Also, the second folding mirror 105b is disposed between the deflection element unit 12 and the second imaging optical element 106b that is closest to the deflection element unit 12 in the second imaging optical system, and the conditional expressions (8’) and (8’’) are satisfied. Thereby, it is possible to provide the optical scanning device 200 that is sufficiently miniaturized by shortening the optical paths of the first and second light fluxes that scan both sides with the deflection element unit 12 interposed therebetween.

[0106] [Third Embodiment] FIG. 7(a) shows a schematic main scanning cross-sectional development view of the optical scanning device 300 according to the third embodiment. Also, FIGS. 7(b) and 7(c) show partial schematic sub-scanning cross-sectional views of the optical scanning device 300 according to the third embodiment. Note that the optical scanning device 300 according to the present embodiment has the same configuration as the optical scanning device 100 according to the first embodiment except that the specifications are different. Therefore, the same members are denoted by the same reference numerals, and the description thereof is omitted.

[0107] Also, the specifications of the optical scanning device 300 according to the present embodiment, the refractive indices and surface intervals of the respective optical elements, and the lens surface shapes of the incident optical element 103 and the imaging optical element 106 are shown in Tables 7, 8, and 9 below, respectively.

[0108]

Table 7

[0109]

Table 8

[0110]

Table 9

[0111] In the optical scanning device 300 according to this embodiment, as shown in FIG. 7(c), the folding mirror 105 reflects the incident light beam downward in the sub-scanning direction, that is, toward the side where the motor 104b and the motor substrate 104c are arranged with respect to the deflection element 104. As a result, it becomes possible to arrange the imaging optical element 106 in the inefficient space formed by the motor 104b and the motor substrate 104c other than the deflection element 104 in the deflection element unit 12. That is, it becomes possible to reduce the size of the optical scanning device 300 according to this embodiment in the sub-scanning cross section.

[0112] FIG. 8 shows the partial magnification deviation at each image height in the optical scanning device 300 according to this embodiment. As shown in FIG. 8, in the optical scanning device 300 according to this embodiment, the maximum partial magnification deviation occurs at the outermost image height, specifically, a partial magnification deviation of about 130.9%. That is, in the optical scanning device 300 according to this embodiment, similar to the optical scanning device 100 according to the first embodiment, the scanning characteristics of the imaging optical system 85 are set such that the scanning speed at each off-axis image height is greater than the scanning speed at the on-axis image height.

[0113] As described above, in the optical scanning device 300 according to this embodiment, the incident optical element 103 has a positive refractive power in the main scanning cross section and converts the incident light beam into a converging light beam in the main scanning cross section. Specifically, in the optical scanning device 300 according to the present embodiment, when the imaging optical system 85 is not virtually provided, the optical path length D between the on-axis deflection point and the position where the on-axis light beam naturally converges in the main scanning cross section m is about 157.8 mm.

[0114] FIGS. 9(a) and (b) show the image height dependencies of the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position on the scanned surface 107 in the optical scanning device 300 according to the present embodiment, respectively. As shown in FIGS. 9(a) and (b), both the main scanning direction LSF depth center position and the sub-scanning direction LSF depth center position are within ±1 mm over the entire image height, indicating that good imaging performance is achieved in the optical scanning device 300 according to the present embodiment.

[0115] In the optical scanning device 300 according to the present embodiment, T c / h = 0.58, D m / T c = 1.26 and f s / f m = 0.08, and the conditional expressions (8), (8a), (9), (9a), (10), and (10a) are satisfied. Also, in the optical scanning device 300 according to the present embodiment, D R2 / T c = 0.32 and |ΔY| = 130.9%, and the conditional expressions (11), (11a), (12), and (12a) are satisfied.

[0116] As described above, in the optical scanning device 300 according to the present embodiment, the folding mirror 105 is disposed between the deflection element unit 12 and the imaging optical element 106 closest to the deflection element unit 12 in the imaging optical system 85, and the conditional expression (8) is satisfied. Thereby, it is possible to provide the optical scanning device 300 that is sufficiently miniaturized by shortening the optical path.

[0117] The numerical values corresponding to the respective conditional expressions in each of the optical scanning devices according to the first to third embodiments are shown in Table 10 below.

[0118]

Table 10

[0119] The preferred embodiments have been described above. However, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist thereof.

[0120] [Image forming apparatus] FIG. 10 shows a partial sub-scanning cross-sectional view of an image forming apparatus 90 including an optical scanning device according to any one of the first to third embodiments.

[0121] The image forming apparatus 90 is a tandem type color image forming apparatus in which an optical scanning unit 11 records image information on a plurality of photosensitive drum surfaces each of which is an image carrier. The image forming apparatus 90 includes an optical scanning unit 11, developing devices 15, 16, 17, and 18, photosensitive drums 23, 24, 25, and 26, a conveyance belt 91, a printer controller 93, and a fixing device 94. Note that the optical scanning unit 11 can be formed by, for example, four optical scanning devices according to the first or third embodiment, or two optical scanning devices according to the second embodiment.

[0122] As shown in FIG. 10, color signals of R (red), G (green), and B (blue) output from an external device 92 such as a personal computer are input to the image forming apparatus 90. Then, the input color signals are converted into respective image data (dot data) of C (cyan), M (magenta), Y (yellow), and K (black) by an internal printer controller 93. Then, the converted image data is input to the optical scanning unit 11.

[0123] From the optical scanning unit 11, modulated light beams 19, 20, 21, and 22 corresponding to each image data are emitted respectively, and the photosensitive surfaces of the photosensitive drums 23, 24, 25, and 26 are scanned in the main scanning direction by the light beams 19, 20, 21, and 22 respectively.

[0124] A charging roller (not shown) for uniformly charging the surfaces of the photosensitive drums 23, 24, 25, and 26 is provided so as to be in contact with the surfaces. Then, the surfaces of the photosensitive drums 23, 24, 25, and 26 charged by the charging roller are irradiated with the light beams 19, 20, 21, and 22 by the optical scanning unit 11. As described above, the light beams 19, 20, 21, and 22 are modulated based on the image data of each color, and an electrostatic latent image is formed on the surfaces of the photosensitive drums 23, 24, 25, and 26 by irradiating the light beams 19, 20, 21, and 22. The formed electrostatic latent image is developed into a toner image by the developing devices 15, 16, 17, and 18 disposed so as to be in contact with the photosensitive drums 23, 24, 25, and 26.

[0125] The toner image developed by the developing devices 15, 16, 17, and 18 is multi-transferred onto a sheet of paper (transfer material) (not shown) conveyed on the conveyance belt 91 by a transfer roller (transfer device) (not shown) disposed so as to face the photosensitive drums 23, 24, 25, and 26. Thereby, a single full-color image is formed. As described above, the sheet of paper onto which the unfixed toner image has been transferred is further conveyed to a fixing device 94 provided behind the photosensitive drums 23, 24, 25, and 26 (the left side in FIG. 10).

[0126] The fixing device 94 is composed of a fixing roller having a fixing heater (not shown) inside and a pressure roller disposed so as to be in pressure contact with the fixing roller. The sheet of paper conveyed from the transfer unit is heated while being pressed by the pressure contact portion between the fixing roller and the pressure roller, whereby the unfixed toner image on the sheet of paper is fixed. Further, a paper discharge roller (not shown) is disposed behind the fixing roller, and the paper discharge roller discharges the fixed sheet of paper outside the image forming apparatus 90.

[0127] Note that as the external device 92, for example, a color image reading device equipped with a CCD sensor may be used. In this case, a color digital copying machine is configured by the color image reading device and the image forming apparatus 90.

[0128] The disclosure of the present embodiment includes the following configurations. (Configuration 1) A deflector that deflects a first light beam from a first light source to scan a first scanned surface in a main scanning direction, and at least one imaging optical element that guides the first light beam deflected by a first deflection surface of the deflector to the first scanned surface. A first imaging optical system, and a first reflection optical element that is disposed between the deflector and a first imaging optical element that is the closest to the deflector among at least one imaging optical element included in the first imaging optical system on the optical path of the first light beam from the deflector to the first scanned surface, and reflects the first light beam. The optical path length between a first on-axis deflection point of the first deflection surface on the optical axis of the first imaging optical system and the first scanned surface is T c1 , and the distance between the outermost off-axis image height of the first scanned surface is h 1 When, 0.50 ≦ T c1 / h 1 ≦ 1.00, and an optical scanning device characterized by satisfying the condition. (Configuration 2) The optical scanning device according to Configuration 1, further comprising a first incident optical system that converts a first light beam from a first light source into a converging light beam in a main scanning cross section and makes the converging light beam incident on the first deflection surface. (Configuration 3) The first incident optical system includes a first incident optical element that converts a first light beam from a first light source into a converging light beam in a main scanning cross section and condenses the light beam in a sub-scanning cross section. The optical scanning device according to Configuration 2, characterized by the above. (Configuration 4) When the first imaging optical system is not provided, the optical path length between the first on-axis deflection point and a first convergence point where the first light beam deflected by the first deflection surface converges in the main scanning cross section is D m1 When, 0.50 ≦ D m1 / T c1 ≦ 2.50, and the optical scanning device according to any one of Configurations 1 to 3, characterized by satisfying the condition. (Configuration 5) When the focal lengths in the sub-scanning cross-section and the main-scanning cross-section of the first imaging optical system are f s1 and f m1 respectively, the optical scanning device according to any one of Configurations 1 to 4, characterized in that the condition 0.05 ≤ f s1 / f m1 ≤ 0.25 is satisfied. (Configuration 6) The optical path length between the first on-axis deflection point on the optical axis of the first imaging optical system and the exit surface of the second imaging optical element that is farthest from the deflector among at least one imaging optical element included in the first imaging optical system is D R2_1 When this is the case, the optical scanning device according to any one of Configurations 1 to 5, characterized in that the condition 0.15 ≤ D R2_1 / T c1 ≤ 0.50 is satisfied. (Configuration 7) The optical scanning device according to any one of Configurations 1 to 6, characterized in that the scanning speed of the first light beam on the first scanned surface increases monotonically from the on-axis image height toward the outermost off-axis image height. (Configuration 8) The value of the ratio of the partial magnification at the outermost off-axis image height to the partial magnification at the on-axis image height is ΔY 1 (%), and the optical scanning device according to Configuration 7, characterized in that the condition 110.0 ≤ ΔY 1 ≤ 140.0 is satisfied. (Configuration 9) A second imaging optical system including at least one imaging optical element that guides the second light beam deflected by the second deflection surface of the deflector to the second scanned surface, and on the optical path of the second light beam from the deflector to the second scanned surface, between the deflector and the third imaging optical element that is closest to the deflector among at least one imaging optical element included in the second imaging optical system, and a second reflective optical element that reflects the second light beam. The deflector deflects the second light beam from the second light source to scan the second scanned surface in the main scanning direction. The optical path length between the second on-axis deflection point of the second deflection surface on the optical axis of the second imaging optical system and the second scanned surface is T c2 , the distance between the outermost off-axis image heights of the second scanned surface is h 2 When this is the case, the optical scanning device, characterized in that 0.50 ≤ T c2 / h 2The optical scanning device according to any one of Configurations 1 to 8, characterized by satisfying the condition of ≦1.00. (Configuration 10) The deflector includes a deflection element having a plurality of deflection surfaces and a drive unit that rotates the deflection element around a rotation axis. The first light beam deflected by the first deflection surface is reflected by the first reflection optical element to the side where the drive unit is disposed with respect to the deflection element in the sub-scanning direction. The optical scanning device according to any one of Configurations 1 to 9. (Configuration 11) The first imaging optical system is composed of a first imaging optical element. The optical scanning device according to any one of Configurations 1 to 10. (Configuration 12) On the optical path of the first light beam from the deflector to the first scanned surface, no reflection optical element other than the first reflection optical element is disposed. The optical scanning device according to any one of Configurations 1 to 11. (Configuration 13) An image forming apparatus comprising: the optical scanning device according to any one of Configurations 1 to 12; a developing device that develops an electrostatic latent image formed on the first scanned surface by the optical scanning device into a toner image; a transfer device that transfers the developed toner image to a transfer material; and a fixing device that fixes the transferred toner image to the transfer material. (Configuration 14) An image forming apparatus comprising: the optical scanning device according to any one of Configurations 1 to 12; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device.

Description of Reference Numerals

[0129] 12 Deflection element unit (deflector) 85 Imaging optical system (first imaging optical system) 100 Optical scanning device 101 Light source (first light source) 104a Deflection surface (first deflection surface) 105 Fold-back mirror (first reflection optical element) 106 Imaging optical element (first imaging optical element) 107 Scanned surface (first scanned surface)

Claims

1. A deflector that deflects a first light beam from a first light source and scans a first scanned surface in a main scanning direction, A first imaging optical system including at least one imaging optical element that guides the first light beam deflected by a first deflection surface of the deflector to the first scanned surface, A first reflective optical element that is disposed between the deflector and a first imaging optical element closest to the deflector among the at least one imaging optical element included in the first imaging optical system on an optical path of the first light beam from the deflector to the first scanned surface and reflects the first light beam, Let the optical path length between the first on-axis deflection point of the first deflection plane on the optical axis of the first imaging optical system and the first scanned surface be T ｃ１ and the distance between the outermost image heights of the first scanned surface be h １ When this is the case 0.50 ≤ T ｃ１ / h １ ≤ 1.00 An optical scanning device, characterized in that it satisfies the following conditions.

2. The optical scanning device according to claim 1, further comprising a first incident optical system that converts the first light beam from the first light source into a converging light beam in a main scanning cross-section and makes it incident on the first deflection surface.

3. The optical scanning device according to claim 2, wherein the first incident optical system includes a first incident optical element that converts the first light beam from the first light source into the converging light beam in the main scanning cross-section and condenses the light beam in a sub-scanning cross-section.

4. The optical path length between the first on-axis deflection point when the first imaging optical system is not provided and the first convergence point at which the first light beam deflected by the first deflection surface converges within the main scanning cross section is D ｍ１ When it is defined as 0.50 ≤ D ｍ１ / T ｃ１ ≤ 2.50 The optical scanning device according to claim 1, characterized in that it satisfies the following conditions.

5. When the focal lengths in the sub-scanning cross section and the main scanning cross section of the first imaging optical system are f ｓ１ and f ｍ１ respectively, 0.05 ≤ f ｓ１ / f ｍ１ ≤ 0.25 The optical scanning device according to claim 1, characterized in that it satisfies the following conditions.

6. When the optical path length between the first on-axis deflection point on the optical axis of the first imaging optical system and the exit surface of the second imaging optical element, which is the farthest from the deflector among the at least one imaging optical element included in the first imaging optical system, is D Ｒ２＿１ and 0.15 ≤ D Ｒ２＿１ / T ｃ１ ≤ 0.50 The optical scanning device according to claim 1, characterized in that it satisfies the following conditions.

7. The optical scanning device according to claim 1, wherein a scanning speed of the first light beam on the first scanned surface monotonically increases from an on-axis image height toward the outermost off-axis image height.

8. The value of the ratio of the partial magnification at the outermost image height to the partial magnification at the on-axis image height is defined as ΔY １ when it is expressed as (%) 110.0 ≤ ΔY １ ≤ 140.0 The optical scanning device according to claim 7, characterized in that it satisfies the following conditions.

9. A second imaging optical system including at least one imaging optical element that guides a second light beam deflected by a second deflection surface of the deflector to a second scanned surface, A second reflective optical element that is disposed between the deflector and a third imaging optical element closest to the deflector among the at least one imaging optical element included in the second imaging optical system on an optical path of the second light beam from the deflector to the second scanned surface and reflects the second light beam, The deflector deflects the second light beam from a second light source and scans the second scanned surface in the main scanning direction, Let the optical path length between the second on-axis deflection point of the second deflection plane on the optical axis of the second imaging optical system and the second scanned surface be T ｃ２ and the distance between the outermost image heights on the second scanned surface be h ２ When this is the case 0.50 ≤ T ｃ２ / h ２ ≤ 1.00 The optical scanning device according to claim 1, characterized in that it satisfies the following conditions.

10. The deflector includes a deflection element having a plurality of deflection surfaces and a drive unit that rotates the deflection element around a rotation axis. The optical scanning device according to claim 1, wherein the first light beam deflected by the first deflection surface is reflected by the first reflective optical element in the sub-scanning direction to the side of the deflection element where the drive unit is disposed. **Claim 11** The optical scanning device according to claim 1, wherein the first imaging optical system includes the first imaging optical element. **Claim 12** The optical scanning device according to claim 1, wherein no reflective optical element other than the first reflective optical element is disposed on the optical path of the first light beam from the deflector to the first surface to be scanned. **Claim 13** An image forming apparatus comprising: the optical scanning device according to any one of claims 1 to 12; a developing device that develops an electrostatic latent image formed on the first surface to be scanned by the optical scanning device into a toner image; a transfer device that transfers the developed toner image onto a transfer material; and a fixing device that fixes the transferred toner image onto the transfer material. **Claim 14** An image forming apparatus comprising: the optical scanning device according to any one of claims 1 to 12; and a printer controller that converts a signal output from an external device into image data and inputs the image data to the optical scanning device.

Images